Spills of hydrocarbons into soil, hydrocarbon gases generated by materials in land fills, and residual vapors in empty storage tanks must be extracted and disposed of to prevent environmental impact through air pollution, toxic hazard, or explosion hazard. Typical systems for achieving this end employ vacuum pumps to create a pressure gradient through perforated pipe embedded in the contaminated soil or land fill material, or lines running to an empty storage tank. The vaporized hydrocarbons are drawn through the vacuum pump into a combustion unit where they are eliminated by burning.
An improved system disclosed in U.S. Pat. No. 4,846,134 employs an internal combustion engine which provides vacuum to the system through the intake manifold of the engine. The extracted waste hydrocarbons provide all or some of the fuel for the engine and are destroyed by combustion in the cylinders. This system provides unique advantages in that supplemental power requirements are minimized for operation of the system.
The control system for starting the engine on a supplemental fuel and mixing the extracted vapor with the supplemental fuel for combustion has previously employed manual control. Valves connecting the supplemental fuel and the hydrocarbon vapor source to the engine have been controlled by a human operator to provide optimum mixture of the fuel, comprising the supplemental fuel and hydrocarbon vapors, and air drawn both from the hydrocarbon vapor source and the atmosphere.
Such operation requires trained operators and full time monitoring of the system to provide optimum efficiency. For cost reduction and efficiency improvement, it is desireable to provide a control system for the vapor extraction system which is automated and provides a proper mixture to the engine for most efficient destruction of the hydrocarbons and minimum pollution from the exhaust gases of the engine.